Routing protocol within hybrid-cellular networks

ABSTRACT

In order to set up efficient routes between two closely-located nodes an optimized route for two nodes within a hybrid-cellular network (HCN) is achieved by converting an HCN route to an ad-hoc route. Thus, a node within the communication system may originally be communicating with another node via an HCN route and then instructed to switch to a more efficient ad-hoc route for communication with the node.

FIELD OF THE INVENTION

The present invention relates generally to ad-hoc wireless networks withapplication to cellular networks, and in particular, to a routingprotocol within hybrid-cellular networks.

BACKGROUND OF THE INVENTION

In a traditional cellular network, mobile units establish directdownlink and uplink connections with a backbone network access pointsuch as a cellular base station (BTS). A recently proposedhybrid-cellular network (HCN) seeks to alleviate the limitations oftraditional cellular systems by allowing uplink and downlink connectionsto involve more than one link, with all links utilizing (i.e., passingthrough) a network coordinator. Such a system is a hybrid betweencellular and ad hoc network architectures, where uplink and/or downlinkdata is relayed to and from the network coordinator by other mobileunits or dedicated repeaters. An example of HCN 100 is depicted inFIG. 1. As is evident, communication to/from base station 102 may existeither as a direct link to the mobile unit (as with mobile unit 101) ormay have one or more intermediate relays (as with mobile unit 104 beingrouted through mobile unit 103). With the introduction of intermediaterelays, long-range transmission can be broken into several shorter-rangelinks, allowing for a reduction in the BTS transmission power on thedownlink and increasing capacity of the uplink.

A major challenge in constructing a hybrid-cellular network isimplementing an efficient routing protocol. The process of routing in anetwork from a node A1 to a node A2 consists of establishing a sequenceof intermediate nodes that are used as relays to transmit informationfrom node A1 to node A2, and from node A2 to node A1. Routing can bedirect when no intermediate node is involved from transmitting from nodeA1 to node A2, and from node A2 to node A1. The goal is to create arobust routing protocol capable of maintaining routing information in ahighly mobile network, yet without the overhead of excessive signaling.Most of the research activities on this subject have focused on adaptingad hoc routing protocols, such as Ad hoc On-demand Vector Routing(AODV), Dynamic Source Routing (DSR), and Destination-Sequenced DistanceVector Routing, for use in an HCN. These protocols are efficient forgathering and maintaining routing information in a general ad hocnetwork, involving topology with multiple source-destination pairs, butare needlessly complicated for an HCN topology, where every route has acommon source or destination node. Therefore, a need exists for arouting protocol within a HCN that is less complicated for HCNtopologies, yet is efficient for gathering and maintaining routinginformation. There is also a need for setting up efficient routs betweennodes in such an HCN system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a prior-art hybrid-cellular network.

FIG. 2 is a block diagram of a particular cell for a communicationsystem capable of operating as a traditional cellular system or a hybridcellular system.

FIG. 3 is a flow chart showing the steps necessary to convert from acellular network to a hybrid-cellular network.

FIG. 4 is a flow chart showing operation of a class J network elementduring route discovery.

FIG. 5 is a block diagram of a network element.

FIG. 6 is a flow chart showing route maintenance.

FIG. 7 illustrates route optimization.

FIG. 8 is a flow chart showing route optimization.

DETAILED DESCRIPTION OF THE DRAWINGS

To address the above-mentioned need, a routing protocol for ahybrid-cellular network is disclosed herein. In order to establishrouting to/from a base station within a hybrid-cellular network, eachnetwork element is assigned a “class of operation” based on a receivedsignal strength of the base station. Each network element is allowed tochoose a network element of lower class for relaying information to thebase station. The above routing protocol is an efficient, yetnon-complex means for routing information in a hybrid-cellular network,where every route has a common source or destination node.

In order to set up efficient routes between two closely-located nodes anoptimized route for two nodes within a hybrid-cellular network (HCN) isachieved by converting an HCN route to an ad-hoc route. Thus, a nodewithin the communication system may originally be communicating withanother node via an HCN route and then instructed to switch to a moreefficient ad-hoc route for communication with the node.

In a hybrid-cellular network where all links utilize a networkcoordinator, the present invention encompasses a method for converting ahybrid-cellular route to an ad-hoc route. The method comprises the stepsof determining if two nodes within the hybrid-cellular network are inclose proximity, determining connectivity information for the two nodes,and determining an optimized ad-hoc route between the two nodes. Theoptimized ad-hoc route between the two nodes does not involve thenetwork coordinator. Finally, the hybrid-cellular route is converted toan ad-hoc route by instructing the two nodes to communicate via theoptimized ad-hoc route.

The present invention additionally encompasses a method for converting ahybrid-cellular route to an ad-hoc route within a hybrid-cellularnetwork. The method comprises the steps of determining if the two nodesare in close proximity, determining route information for the two nodes,and determining an optimized ad-hoc route between the two nodes based onthe route information. The optimized ad-hoc route between the two nodescomprises an ad-hoc route having a least amount of hops, and theoptimized ad-hoc route between the two nodes does not involve thenetwork coordinator. Finally, the two nodes are instructed to convertthe hybrid-cellular route to the ad-hoc route by assigning the two nodesthe optimized ad-hoc route.

Finally, the present invention encompasses an apparatus for creating anad-hoc route. The apparatus comprises logic circuitry determining anoptimized ad-hoc route between two nodes utilizing a hybrid-cellularroute. The optimized route is based on route information, and theoptimized ad-hoc route between the two nodes comprises an ad-hoc routehaving a least amount of hops. Additionally, the optimized ad-hoc routebetween the two nodes does not involve the network coordinator. Theapparatus additionally comprises a transmitter instructing the two nodesto change from an HCN route to the ad-hoc route.

Turning now to the drawings, wherein like numerals designate likecomponents, FIG. 2 is a block diagram of a particular cell 200 for acommunication system capable of operating as a traditional cellularsystem or a hybrid cellular system. Cell 200 contains BTS 201 and anumber of mobile or remote units/nodes 203-205 (only three shown). Theset of remote units 203-205 is comprised of the terminals 203-204maintaining active communication with BTS 201 and the terminals 205 thatare in “sleep” mode, i.e., the terminals that are powered on but notmaintaining an active connection with the BTS. Note that a terminal in“sleep” mode can still listen to some channels, such as the pagingchannels or the broadcast channel, but does not transmit any data orcontrol information, so that most of the time the BTS is not even awareof the presence of this terminal in its coverage area. A remote unitcould be stationary or mobile. Cell 200 may also include a number ofstationary repeaters 202, which are specifically deployed for relayingdata between BTS 201 and the active remote units 203-204. BTS 201,remote units 203-205, and stationary repeaters 202 comprise a set ofnetwork elements within a cell.

During operation cell 200 may function as either in standard cellulartelephone mode, standard ad-hoc mode, or in HCN mode. During standardcellular operation all communications between mobile units 203-205 andbase station 201 take place with direct communication between mobileunits 203-205 and base station 201. As discussed above, during HCNoperation, all links either originate, or terminate at BTS 201; howeveruplink and/or downlink data may be relayed to and from BTS 201 by otherremote units or dedicated repeaters. Cell 200 may convert from one modeof operation to another.

As discussed above, a problem exists in establishing a routing protocolthat is efficient in gathering routing information, yet is lesscomplicated than prior-art protocols. In order to address this issue therouting protocol relies on establishing J+1 classes of operation amongthe network elements. BTS 201 is always a class 0 entity, whereas othernetwork elements belong to class 1 through J. At any given time, anetwork element may only belong to a single class, and for uplinktransmissions (i.e., those transmissions that terminate at BTS 201) mayrelay data to only those network elements having a lower value in class.In a similar manner, for uplink transmissions network elements may onlyreceive relayed transmissions from network elements having a greatervalue in class. Thus, for uplink transmissions a network element havingclass x may only relay information received from network elements havingclass >x, and may perform relay transmissions only to network elementshaving class <x.

For downlink transmissions, (i.e., those transmissions that originate atBTS 201) a network element may relay data to only those network elementshaving a higher value in class. In a similar manner, for downlinktransmissions, network elements may only receive relayed transmissionsfrom network elements having a lower value in class. Thus, for downlinktransmissions a network element having class x may only relayinformation received from network elements having class <x, and mayperform relay transmissions only to network elements having class >x.For both uplink and downlink transmissions, class membership isdetermined based on the strength of the received signal from the BTS.

As discussed, it is assumed that the BTS 201 is a common destination onthe uplink, and common source on the downlink, for all routes in a cell.Each route is established by specifying a sequence of links between thenetwork elements. The routes are established sequentially class byclass. Consider the routing procedure for class j network elements. Atthis stage of the protocol, the routes between BTS 201 and all networkelements belonging to classes I through j-1 have been established. Aclass j network element evaluates link quality to at least some, andpreferably all, class 0 through j-1 network elements and establishes alink with the best one. In the first embodiment of the present inventionthe received signal strength from a network element is used as anindicator of the link quality. In alternate embodiments, however, otherlink quality indicators, such as the C/I ratio, C/N, C/(I+N), BER, FER,link loading, or the average path loss are used. The average path lossis most useful as a quality metric when the network elements transmit atvarying power levels. For a given class j network element, only a subsetcomprised of the neighboring class 0 through j-1 network elements needsto be considered.

In an alternate embodiment of this invention, a class j network elementevaluates link quality to at least some, and preferably all, class 0through j-1 network elements and determines a group of potential networkelements for relaying. It establishes a connection with one of thenetwork elements from this group. If at a later point in time, theconnection quality becomes unsatisfactory, the class j network elementmay attempt to establish a connection with another network element fromthis group.

In a further alternate embodiment, a class j network element mayestablish a connection with one of the class 0 through j-1 networkelements based on a cumulative path quality metric announced by thatnetwork element. In the further alternate embodiment, the cumulativepath metric is a sum of link characteristics along the path of thatnetwork element to the BTS. The link characteristics may comprise suchthings as quality metrics for the links, link C/I ratio, C/N, C/(I+N),BER, FER, the average path loss on the links, the amount of trafficflowing through the links (link loading), . . . , etc. The cumulativepath metrics may include a penalty term for the number of hops along thepath to the BTS.

The protocol effectively constructs a spanning tree rooted at theBTS/network controller 201 for all network elements in a given cell.With this construction, every class 1 network element necessarilycommunicates directly with the BTS 201, and, more generally, every classj network element communicates with a single network element of class 0through j-1. Note that links between network elements of the sameclasses are forbidden in order to avoid cycles in the routing graph. Forany link, the lower-class network element is termed the “parent” and thehigher-class network element is termed the “child”. A given networkelement has a single “parent” and can have multiple “children”.

As one of ordinary skill in the art will recognize, any HCN routingprotocol will need to address two related routing tasks: (i) conversionof the network from cellular to HCN topology, and (ii) incrementalupdate of the routes once the HCN topology is established. Theconversion procedure configures the initial HCN, whereas incrementalupdates of the routes adapt to changes in the network.

Conversion from Cellular to HCN Topology

Consider now details of the conversion procedure from cellular to HCNtopology based on the above routing protocol. This conversion processcould occur on a per-cell basis, and does not need to be performedsimultaneously for the whole network. The conversion involves thededicated repeaters and the network elements that are activelymaintaining communication with BTS 201 since network elements that arein “sleep” mode could be incorporated into the HCN by the subsequentincremental updates in the topology. Alternatively, the units in “sleep”mode could be paged and be commanded to participate in the conversionprocess. This embodiment is particularly useful if dedicated repeatersare allowed to transition to “sleep” mode. The conversion, a flowchartof which is shown in FIG. 3, is as follows.

Step 1. Determine HCN membership. On the cellular downlink, BTS 201indicates to all active network elements in the cell that conversion toHCN is to begin by broadcasting a probe signal on the broadcast controlchannel or a new logical channel. BTS 201 then commands every activenetwork element to report back an HCN participation flag. This flagindicates whether a network element is suitable for participation in theHCN. For instance, depending on the state of its battery, its speed orits hardware capabilities, a network element may not be qualified toparticipate. The non-participating network elements continuecommunication with BTS 201 in cellular mode. In order to conservebandwidth, the HCN participation flag can be sent only by networkelements willing to participate in the HCN. Not responding would thenmean that the network element will not participate in the HCN.

Step 2. Determine class membership. BTS 201 commands all networkelements participating in the HCN to determine their particular class ofoperation. This is accomplished by BTS 201 broadcasting a set ofthresholds T₁ through T_(j) to be used by the network elements for classdetermination. This broadcasting can occur at the time when theconversion is initiated, or periodically broadcasted on a controlchannel. In an alternate embodiment the thresholds are hard-coded in thenetwork element. The network elements measure a signal characteristicfor a downlink transmission from BTS 201. In the first embodiment of thepresent invention the downlink received signal strength (RSS) from BTS201 is utilized, however in alternate embodiments other signalcharacteristics such as a Carrier to Interference (C/I) ratio, bit errorrate (BER), frame error rate (FER), . . . , etc. may be utilized. TheRSS is averaged over a sufficient period of time to determine theirclass as follows: if RSS≧T₁, then the network element is a member ofclass 1. If RSS<T_(j), then the network element is a member of class.If, however, if T_(k-1)>RSS≧T_(k), where k is an integer such that1<k<J, then the network element is a member of class-k. Alternatively,BTS 201 could determine the class of the participating network elementsbased on the RSS measurements (or other metrics) obtained on thecellular uplink, and then transmit the class designations to thecorresponding network elements. Additionally, in an alternateembodiment, network elements measure a signal characteristic for adownlink transmission from BTS 201 and report these measurements back tothe BTS 201. The BTS then determines the class for each network elementand informs each network element of its class.

Step 3. Discover route. Upon completion of the class determination step,BTS 201 assigns every participating network element a preferablyuniquely identifiable pilot waveform and commands all participatingelements in cell 200 to participate in a route discovery session (RDS).In an alternate embodiment, the pilot waveforms could be pre-assigned bythe BTS 201 to each network element prior to formation of HCN. Duringthe RDS, each network element will determine a period for transmissionbased on its class of operation and then broadcast a signal (e.g., itspilot) during a pre-determined time period. The signal is utilized byother network elements for choosing a relay. Specifically, the durationof the RDS is divided into J time periods, one for each class 1 throughJ. (Note it is assumed that within a cell all participating networkelements are at least coarsely frame-aligned). In each time period,every network element of the corresponding class transmits its uniquepilot and a control message (the control message may also be modulatedby the pilot waveform). BTS 201 transmits its unique pilot whether ornot in RDS. In addition to transmitting during its time period, eachnetwork element will receive the pilot signals and control messagestransmitted by other network elements in other time periods and thendetermine the class and identity of these network elements. A networkelement of lower class is then chosen that will serve as a relay. In thefirst embodiment of the present invention the network element chosenwill be the one of lower class having a best signal strength as measuredat the “child” network element. In an alternate embodiment, the networkelement chosen will be the one of lower class having a lowest cumulativepath metric. This information will then be made available to BTS 201.

Step 4. Update resource allocation and link establishment. Uponcompletion of route discovery, BTS 201 relies on the topologyinformation gathered during the RDS to allocate resources, such astransmit powers and segments in the space-time-frequency grid, forcommunication links between “children” and their corresponding“parents”. With resources assigned, links between “parents” and theircorresponding “children” are established. In general, the linkestablishment can be centralized (BTS-directed) or decentralized. In thecentralized case, BTS 201 on the cellular downlink directs each“parent“−”child” pair to begin transmission and reception on the link'sassigned resources. In the decentralized case, BTS 201 on the cellulardownlink informs each “parent” of its assigned resources, and each“parent“−”child” pair establishes communication autonomously andasynchronously of other pairs (e.g., using the random access channelprocedure or pre-allocated slots with a contention mechanism).

FIG. 4 is a flow chart showing operation of a class-k network element500 (shown in FIG. 5) during route discovery. For route discovery, it isenvisioned that the pilots are direct sequence spread spectrum waveforms(either in time domain or in frequency domain), and received bytransceiver 501. (Other signaling schemes that are robust againstco-channel interference and amenable to fast acquisition are suitable.)The pilot and control message transmissions could be of relatively lowpower, unless they are destined for BTS 201, since only the neighboringnetwork elements need to exchange routing information. In practice,logic circuitry 502 (e.g., a computer program executingcomputer-readable code, or a microprocessor controller executingembedded instructions) is provided to analyze received pilots anddetermine those network elements acceptable for routing data. Inparticular, logic circuitry 502 serves as means for determining a signalcharacteristic of a transmission from a base station, means fordetermining a particular class of operation for network element 500,means for choosing a network element having a lower class of operationfor routing data, and means for routing the data through the networkelement having the lower class of operation.

The logic flow begins at step 400 where logic circuitry 502 analyzes asignal characteristic of a transmission from a base station anddetermines a particular class (e.g., class k) of operation. At step 401logic circuitry 502, monitors pilot and control message transmissionsfrom lower-class network elements (including class 0 BTS 201) in periods1 through k-1. The logic circuitry 502 then determines a “parent” (step403) whose class is <k. As discussed above, the parent is chosen to bethe class 0 through k-1 network element with the best-received signal atthe class-k network element. In an alternate embodiment, the logiccircuitry 502 evaluates a cumulative path metric of routes to the BTSthrough one of the lower-class network elements, and picks a lower classnetwork element with the lowest cumulative path metric as its “parent”.In the kth time period, transceiver 501 transmits its unique pilot andthe control message (step 405) Note that for a class J network element,transmission of the pilot is not necessary, but transmission of acontrol message indicating its choice of the “parent” is still required.In the control message, the network element announces its own class(note that this announcement can be implicit since only class-k networkelements will be transmitting during this time period), announces its“parent”, and, according to an alternate embodiment, includes cumulativemetric of its path to the BTS. In the k+1 through J time periods, logiccircuitry 502 monitors the control message announcements fromhigher-class network elements and determines its “children”. At thecompletion of the RDS, assuming that all control messages reach theirintended destinations, every network element is aware of its “parent”and its “children”. BTS 201 determines the topology of the HCN bypolling network elements on the cellular downlink. Note that this stepis not necessary if BTS 201 has successfully received all messagesexchanged during the RDS. When the topology is known by the system,standard HCN routing for uplink transmissions (i.e., data originating ata network element, destined for BTS 201) then takes place by logiccircuitry 502 routing the data through the network element having thelower class of operation (as chosen above). In particular, a networkelement chosen for routing will have its logic circuitry 502 receiveuplink data from network elements of higher class of operation (i.e.class>k), and then route the received data to network elements having alower class of operation.

In a similar manner, routing for downlink transmissions (i.e., dataoriginating at a BTS 201 having a final destination at a networkelement) takes place by logic circuitry 502 routing the data receivedfrom the network element having the lower class of operation. Inparticular, a network element chosen for routing will have its logiccircuitry 502 receive downlink data from network elements of lower classof operation, and then route the received data to network elementshaving a higher class of operation.

Note that the RDS is a serial process: the pilot waveforms and controlmessages from network elements of lower classes must be received beforethe messages from network elements of higher classes. This conditionallows the routing tree to be built sequentially from the BTS 201 first,down to the network elements of class J.

As described above with reference to FIG. 3, each network element isassigned a unique pilot waveform. The pilot assignments are not based onthe class memberships of the network elements. Hence, during each RDSperiod a network element needs to monitor the entire set of pilotwaveforms in order to learn of its parent or children nodes. To reducethe set of possible pilot waveforms to be searched during each RDSperiod, the set of pilot waveforms can be partitioned into J subsets,one for each class. With such an assignment, only the j-th subset needsto be searched during the j-th RDS period. The allocation of the subsetscan be pre-determined or dynamically assigned by BTS 201 and announcedto the participating network elements. To facilitate class-based pilotassignment, BTS 201 might need to receive class reports from theparticipating network elements. This could be efficiently performed byincluding the class reports with the HCN participation flags. Note that,although the class-based pilot assignment leads to reduced searchcomplexity, it also results in increased signaling overhead since pilotwaveforms need to be reassigned upon class changes of the networkelements.

The network elements that were unable to establish an HCN route due tolink establishment failure continue to communicate directly with BTS201. They may attempt to participate in the HCN during subsequent RDS.The network elements that are participating in the HCN tear down theircellular data channels and begin transmitting and receiving data usingtheir HCN routes. Alternatively, the HCN can be used on the uplink ordownlink only, while the other link remains in cellular mode. Forfurther control messaging from BTS 201, the downlink control channelstructure remains in place for all active network elements(participating in the HCN and non-participating).

Note also that a network element may decide to use the HCN mode fortransmitting while not relaying any transmission. This could happen whenthe battery life of the terminal is low, or because the subscriberowning this network element configured it not to relay any calls. Inthis case, the network element will force its class to be “class J” instep two of FIG. 3. The other steps of the algorithm described in FIG. 3remain the same. Alternatively, such a network element could receive allthe messages from the other network elements but does not broadcast anypilot waveform or control message. When such a network element needs totransmit, it needs to send the routing path to the BTS so that the BTSknows how to reach it.

Route Maintenance

A route maintenance procedure (RMP) is necessary for coping with changesin HCN membership and topology. The route maintenance procedureBTS-initiated and is performed periodically in each cell, typicallyevery few superframes. The time interval between updates should besufficiently short to track changes in membership and topology of thenetwork. In an alternate embodiment, RMP could be triggered upon achange of HCN membership.

A change in the HCN membership, for instance, can be due to arrival of anew network element into the cell, due to transition of a networkelement from “sleep” to active mode, or due to departure of a networkelement from the cell. Furthermore, the HCN membership will change ifBTS 201 attempts to involve the network elements that are in “sleep”mode or dedicated repeaters into the HCN. A change in the HCN topology,for instance, can be due to a change in class memberships of theparticipating network elements. It is envisioned that a proceduresimilar to the above four-step HCN conversion procedure is performedperiodically for route maintenance. The steps are as follows, and shownin FIG. 6:

Step 1. Update HCN membership. Using the cellular downlink controlchannels, BTS 201 indicates to all active network elements in the cellthat the route maintenance procedure is to begin. BTS 201 then commandsevery active but not previously participating network element to reportback a participation flag. Note that all active non-participatingnetwork elements necessarily maintain two-way communication with BTS 201in cellular mode. All previously participating network elements do notretransmit their participation flag, unless class-based pilot assignmentis performed. In this case, each network element with a change in classalso transmits an HCN participation flag. BTS 201 can involve a networkelement in “sleep mode” or a repeater network element into the HCN bypaging and commanding the network element to report back an HCNparticipation flag.

Step 2. Update class membership. BTS 201 commands all network elementsparticipating in the HCN to determine their class. The network elementsdetermine their class as described in Step 2 of the above HCNinitialization procedure.

Step 3. Update route discovery. Upon completion of the classdetermination step, BTS 201 assigns every newly participating networkelement a uniquely identifiable pilot waveform and commands all elementsin the HCN to participate in RDS, as specified in Step 3 of the aboveHCN initialization procedure. In an alternate embodiment, pilotwaveforms are assigned prior to performing RMP. All previouslyparticipating network elements that have since become inactive orineligible to participate in the HCN remain silent during the RDS.

Note that by maintaining silence during the RDS, these network elementsare effectively excluded from participation in the HCN. To continuecommunication with BTS 201, they switch to cellular communication modepreferably by means of a BTS 201 uplink random access channel.

Step 4. Update resource allocation and link establishment. This step isidentical to Step 4 of the HCN initialization procedure.

Route Failure Recovery

A periodically performed route maintenance procedure provides anefficient mechanism for recovery from route failures. That is, an HCNparticipating network element whose route is disrupted simply monitorsBTS 201 downlink control channel for an announcement of the next routemaintenance procedure. By participating in the next route maintenanceprocedure the network element establishes a new HCN route. If a networkelement is repeatedly unsuccessful in establishing an HCN route throughroute maintenance procedures, it enters a cellular operating mode bymeans of BTS 201 uplink random access channel. Alternatively, a routefailure could be an event that triggers an RDS.

HCN Handoff Operation

Inter-cell hand-off for participating network elements is essentiallythe same as inter-cell hand-off in cellular mode. Specifically, allparticipating network elements maintain a list of candidate BTSs forinter-cell handoff. To establish a communication link with a new BTS, aparticipating network element first accesses the new BTS using thatBTS's uplink random access channel. At this stage, a (low) data ratechannel is established in cellular mode with the new BTS. Uponestablishing the cellular link in the new serving cell, the networkelement tears down its HCN connection in the old cell. Once the cellularlink in the new cell is established, if applicable, the network elementparticipates in the route maintenance procedure for the new servingcell. Note that during the handoff process, the network element mightexperience a lower data rate until it participates in the routemaintenance procedure and joins the HCN network in the new cell.Alternatively, a network element arriving could trigger a full RDS. Or,the arriving network element could be prevented to transmit until thenext RDS.

Powering Off Procedures

Consider a “parent” network element, which is being powered off by itsowner. In this case, a new route to the BTS needs to be discovered byall “children” nodes that are communicating with the BTS through this“parent” node. In the first embodiment of this invention, these“children” nodes, upon terminating their connections with the poweredoff “parent” node, simply monitor the downlink control channel andparticipate in the following RMP session. In a second embodiment, the“parent” network element sends to the BTS a “power off” flag. The BTSthen immediately initiates RMP. In another embodiment, the “children”re-establish direct communication with the BTS until the next regularlyscheduled RMP period. In yet another embodiment, the powering off anetwork element is delayed until the next periodic route discoverysession.

Efficient Routing Procedure

The establishment of any HCN may result in inefficient communicationwhen two nodes in the HCN need to communicate with each other. Forexample a light switch may be paired with a light fixture that itcontrols, or a thermostat paired with an air valve in an HVACapplication. If the devices that are being paired are not in range ofeach other it is very difficult to optimize routes between paireddevices during the association process, as a result the routes betweenpaired devices may be very inefficient causing extra traffic across thenetwork. This is illustrated in FIG. 7.

As shown in FIG. 7, network coordinator 701 serves as a centralcontroller (i.e., class zero) for the network, and as such traffic inthe network flows to and from the root of the tree. In some applicationsit is necessary to pair devices (other than network coordinator 701) inthe network together because they are required to exchange messages tocomplete a task. In this situation the devices will exchange messageswith each other through network coordinator 701. This route may beinefficient. For example, if node 702 needs to communicate with node704, it will be inefficient to route communication through networkcoordinator 701 (5-hop route). As is obvious, the best route would be a2-hop route through node 703 and then directly to node 704, bypassingnetwork coordinator 701. In the preferred embodiment of the presentinvention the network automatically adjust the tree structure whendevice pairings need to be made. In particular, when two nodes under anetwork coordinator need to communicate, standard HCN routing proceduresare suspended, with an ad-hoc route being established between the twonodes. A flow chart showing this procedure is shown in FIG. 8.

The logic flow begins at step 801 where a network is in operationutilizing an HCN routing procedure as discussed above. At step 803network coordinator 701, and in particular, transceiver 501 receives arequest to establish a pairing between two nodes (e.g., nodes 702 and704). In an alternate embodiment, a hybrid-cellular route may alreadyexist between the two nodes, and the communication system may wish toconvert the HCN route to a more-efficient ad-hoc route.

At step 804 a determination is made by logic circuitry 502 whether ornot the two nodes are located in close proximity to each other. In itssimplest form, this step simply comprises determining if both nodes areunder the same network coordinator. However, other methods may beutilized to determine if the nodes are in close proximity to each other.For example, the physical location of each device may be determined, andinformation on the proximity of the two devices may be determined fromthe physical location of each device. Additionally, the class of eachdevice may be determined, and the physical location of each device maybe inferred from the device's class. Regardless of how the determinationis made, the logic flow only continues if the two devices are in closeproximity to each other. Thus, the logic flow continues to step 805 whenthe two devices are in close proximity to each other, otherwise thelogic flow ends at step 811.

Continuing, at step 805 network coordinator 701 (via logic circuitry502) determines connectivity, or route information for nodes incommunication with network coordinator 701. In the preferred embodimentof the present invention network coordinator 701 accesses a database(not shown in FIG. 5) containing all nodes in the network, and neighbortables for each node in the network. If such connectivity information isnot available, network coordinator 701 will request the information fromdevices in the network. This information comprises such information astree route path for link between 702 and 704, and a neighbor list andassociated link quality for nodes along tree route path. From the aboveinformation network coordinator 701 can determine if a shorter routepath is available between 702 and 704, and inform the nodes along thepath of the new link/pairing.

Once network coordinator 701 has the information on the devices beingpaired, and connectivity data on the devices in the network, then atstep 807 network coordinator 701 determines an optimized route betweenthe paired devices. The optimal route between the pair may be affectedby several parameters such as number of hops, link quality, number ofredundant paths etc. These parameters are weighted a-priori andprogrammed into any network coordinator's optimization algorithm. In thepreferred embodiment of the present invention the optimal routecomprises a route with a least amount of hops.

It should be noted that in some instances, the optimal route may be thecurrent HCN route utilized between the two devices. Because of this, atstep 808 a determination is made whether or not a better route existsbetween the two devices. In other words, at step 808 a determination ismade as to whether or not the HCN route can be improved upon. If this isthe case, the logic flow continues to step 809, otherwise the logic flowends at step 811.

At step 809 the pairing is made. In other words, if an HCN route alreadyexists, the HCN route is converted to the better ad-hoc route. If,however, no route previously existed between the two devices, the ad-hocroute is simply established. In particular, at step 809, the networkcoordinator 701 has determined the optimal ad-hoc path between thepaired nodes 702 and 704. Having determined the optimal path the networkcoordinator 701 informs/instructs (via transceiver 501) each node on thepath of the pairing and the next hop to route the message. In thepreferred embodiment of the present invention the network coordinatorwill send a message to node 702 which pairs 702 with node 704 andincludes the next hop node as node 703. The network coordinator thensends a message to node 703 informing node 703 that a pairing betweennodes 702 and 704 exists and that the next hop to destination 704 isnode 704, and the next hop to destination 702 is node 702. In responseto this message node 703 stores the next hop information for both node702 and 704 in a routing table. This procedure continues along the pathbetween the paired nodes (702 and 704) until all nodes on the path areaware of the new routing information.

The above procedure optimizes routing for two nodes within an HCNcommunication system by converting HCN routes to ad-hoc routes. Thus, anode within the communication system may be originally communicatingwith another node via an HCN route and then be instructed to switch to amore efficient ad-hoc route for communication with the node. It shouldbe noted that if the pairing procedure is initiated through networkcoordinator 701, then the optimization of the tree could be done beforethe pairing procedure is initiated. This order of events could savetraffic on the network since a reorganization of the tree structure willcause changes in the logical addresses of devices in the network, whichcould cause changes in the previously established pairing and generateextra control traffic on the network.

While the invention has been particularly shown and described withreference to a particular embodiment, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention. Itis intended that such changes come within the scope of the followingclaims.

1. In a hybrid-cellular network where all links utilize a networkcoordinator, a method for converting a hybrid-cellular route to anad-hoc route, the method comprising the steps of: determining if twonodes within the hybrid-cellular network are in close proximity;determining connectivity information for the two nodes; determining anoptimized ad-hoc route between the two nodes, wherein the optimizedad-hoc route between the two nodes does not involve the networkcoordinator; and converting the hybrid-cellular route to an ad-hoc routeby instructing the two nodes to communicate via the optimized ad-hocroute.
 2. The method of claim 1 further comprising the step of receivinga request to establish the pairing between the two nodes.
 3. The methodof claim 1 wherein the step of determining if the two nodes are in closeproximity comprises the step of determining if the two nodes are under asame network coordinator.
 4. The method of claim 1 wherein the step ofdetermining connectivity information comprises the step of determininginformation taken from the group consisting of a tree route path betweenthe two nodes, a neighbor list for each node, and an associated linkquality for nodes along the tree route path.
 5. The method of claim 1wherein the step of determining the optimized ad-hoc route comprises thestep of determining a route with a least amount of hops.
 6. In ahybrid-cellular communication system where all links utilize a networkcoordinator, a method for converting a hybrid-cellular route to anad-hoc route, the method comprising the steps of: determining if the twonodes are in close proximity; determining route information for the twonodes; determining an optimized ad-hoc route between the two nodes basedon the route information, wherein the optimized ad-hoc route between thetwo nodes comprises a ad-hoc route having a least amount of hops,wherein the optimized ad-hoc route between the two nodes does notinvolve the network coordinator; and instructing the two nodes toconvert the hybrid-cellular route to the ad-hoc route by assigning thetwo nodes the optimized ad-hoc route.
 7. The method of claim 6 furthercomprising the step of receiving a request to establish the pairingbetween two nodes.
 8. The method of claim 6 wherein the step ofdetermining if the two nodes are in close proximity comprises the stepof determining if the two nodes are under a same network coordinator. 9.The method of claim 6 wherein the step of determining route informationcomprises the step of determining information taken from the groupconsisting of a tree route path between the two nodes, a neighbor listfor each node, and an associated link quality for nodes along the treeroute path.
 10. A method comprising the steps of: communicating to anode via an HCN route utilizing a network coordinator; receiving aninstruction to communicate via a more-efficient ad-hoc route; andcommunicating to the node via the ad-hoc route, wherein the ad-hoc routedoes not use the network coordinator.
 11. A network coordinator existingwithin a hybrid-cellular network where all links utilize the networkcoordinator, an apparatus for creating an ad-hoc route, the apparatuscomprising: logic circuitry determining an optimized ad-hoc routebetween two nodes utilizing a hybrid-cellular route, the optimized routebeing based on route information, and wherein the optimized ad-hoc routebetween the two nodes comprises an ad-hoc route having a least amount ofhops, and wherein the optimized ad-hoc route between the two nodes doesnot involve the network coordinator; and a transmitter instructing thetwo nodes to change from an HCN route to the ad-hoc route.
 12. Theapparatus of claim 11 further comprising a receiver receiving a requestto establish the pairing between two nodes comprises a request from afirst node to establish a pairing with a second node.